FLT3 and acute myeloid leukemia: The utility of pS6 as a biomarker for the efficacy of midostaurin against wt FLT3‐expressing AML was investigated by comparing drug effects on pS6 in AML cell lines that were around 2‐fold or more sensitive to midostaurin (Kasumi‐1‐luc+, K052, OCI‐AML2) than other AML cell lines (HEL, OCI‐AML3).